Lightning arrester

ABSTRACT

A step-up transformer is combined with a multiple-electrode gasfilled discharge tube to provide a pulse of sufficient magnitude to fire the tube and thereby protect a signal line and the equipment to which it is connected against voltage surges which may be harmful but which are otherwise too low to ignite the tube.

United States Patent [191 Crask et al.

[ June 11, 1974 LIGHTNING ARRESTER [75] Inventors: Roy I. Crask, Edina; William D.

Egerer, Minneapolis, both of Minn.

[73] Assignee: Buckbee-Mears Company, St. Paul,

Minn.

[22] Filed: Dec. 26, 1972 [211 App]. No.: 318,098

[52] US. Cl 317/16, 315/DIG.5, 315/276, 317/31, 317/50, 317/51, 317/62, 317/76 [51] Int. Cl. H02h 3/22 [58] Field of Search 317/61.5, 62, 73, 76, 16, 317/31, 50, 51; 3l5/DIG. 5, 276

[56] References Cited I UNITED STATES PATENTS 2,967,256 1/1961 -Rees ..'317/62X 3,403,293 9/1968 Michelsen 3l5/DlG. 5

Primary Examiner-James D. Trammell Attorney, Agent, or FirmJacobson and Johnson 5 ABSTRACT A step-up transformer is combined with a multipleelectrode gas-filled discharge tube to provide a pulse of sufficient magnitude to fire the tube and thereby protect a signal line and the equipment to which it is connected against voltage surges which may be harmful but which are otherwise too low to ignite the tube.

6 Claims, 2 Drawing Figures UTILIZATION DEV 1CE 1 LIGHTNING ARRESTER 1. Field of the Invention This invention is directed for use in the field of lightning arresters or protectors to be used for protecting electrical signal lines against voltage surges which may be induced or otherwise coupled to the line and which could harm equipment of personnel if not arrested.

2. Description of the Prior Art An article titled New Gas Tube Protector Technique forCircuits by C. Bruce Barksdale appearing in Telephony on Oct. 17, 1970 describes in some detail the more commonly used means of protecting electrical lines against induced lightning surges. Briefly, this article describes the use of a gas-filled discharge tube containing three electrodes with one of the electrodes grounded and the other 'two electrodes connected to respective ones of a pair of signal lines, such as a twowire telephone line. Types of suitable gas-filled discharge tubes and their manner of construction and operation are described in US. Pat. Nos. 3,522,570 and 3,535,779 by Wanaselja. A high magnitude pulse, such as that induced in a telephone line by a nearby lightning stroke will; if of a magnitude that equals or exceeds the ignition or firing threshold of a gas tube, cause the tube to conduct thereby providing apath to ground for both lines thus preventing this high surge from reaching the equipment being fed by the signal lines, such as a telephone receiver and transmitter. Both lines are grounded because all of the electrodes are contained in a single cavity and once the gas ignites in the cavity it brings all of the electrodes to the same low potential level. A major drawback of the multipleelectrode gas-filled discharge tube is its relatively high igniting potential which is ordinarily in the range of at least 200 volts and more often is in the range of 300 to 500 volts. While this range may be suitable for protection against harm to heavy equipment and even possibly protect against harm to life, voltage surges of a lesser magnitude which are not arrested can still cause a great deal of harm to other present day equipment, especially equipment containing low voltage transistors and other semiconductor devices. Also, there is still the potential danger of injury to personnel from voltage surges which have a magnitude less than the ignition or firing potential levels.

SUMMARY OF THE INVENTION In a multiple-electrode gas-filled discharge tube used- BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates a preferred embodiment of the invention; and

FIG. 2 illustrates a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, a pair of signal lines 10 and 11 feed a utilization device 12. A five-electrode gasfilled discharge tube 13, is also connected across signal lines 10 and 11. One electrode 14 is connected directly to signal line 10; another electrode 15 is connected to line 11; and a third electrode 16 which may be the outer casing is connected to electrical ground. The tube 13 also contains a fourth electrode 17 which is associated with electrode 14 and a fifth electrode which is associated with electrode 15. The primary winding of a transformer 19 is connected to electrode 14 and the secondary winding is connected to electrode 17. The primary winding of another transformer 20 is connected to electrode 15 and its secondary is connected to electrode 18. Each transformer has a step-up turns ratio and is polarized to produce the maximum potential difference between its associated electrodes when a signal appears at the respective electrodes 14 and 15 which are directly connected respectively to lines 10 and 11.

Under normal operating conditions, when the electrical signal on signal lines 10 or 11 is the usual or normal signal level, the signal is applied to and utilized by utilization device 12. When the voltage surge which substantially exceeds the normal signal magnitude appears on signal line 10, it is applied to electrode 14. Without transformer 19 in the electrical circuit, the surge would have to be a magnitude at least equal to the firing potential of the gas tube 13', otherwise, the surge will be transmitted down signal line 10 to the utilization device 12. As stated earlier, in the ordinary case the firing potential of gas tube 13 is at least 300 to 500 volts. In the arrangement illustrated in FIG. 1, the surge appearing on signal line 10 is also applied to electrode 17 through the step-up transformer 19. If the magnitude of the potential applied in this fashion across the electrodes 14 and 17 is equal to or exceeds the igniting potential of the gas tube 13, the gas tube will fire to bring the signal line 10 down virtually to the ground signal level of electrode 16, except for the potential drop across the tube. The turns ratio of transformer 19 is selected such that the signal on line 10 can exceed the normal signal by a predetermined amount, for example, up to a level that will not harm the utilization device 12, and not fire the gas tube 13 but when the signal exceeds or nears a level which may be harmful, then the potential difference across electrodes 14 and 17 will be sufficient to ignite the gas tube 13. For example, if gas'tube 13 has an igniting potential in the order of about 480 volts, and the normal signal level on line 10 ranges up to about 5 volts, and it is desired to arrest any signal on line 10 which exceeds 6 volts, the turns ratio should be in the order of about to I so that a 6-volt signal appearing at electrode 14 from line 10 will produce about 480 volts across electrodes 14 and 17 thereby igniting the gas tube 13. A signal level ranging between 5 and 6 volts, which is assumed to be an acceptable level, will not be arrested because it will not cause the gas tube to fire. In the event of a large enough surge on line 11, it will cause the gas tube 13 to fire inthe same manner through the operation of transformer 20 connected between electrodes 15 and 18. So in a two-line transmission system, for example, a two wire telephone line system, a five electrode gas-filled discharge tube in combination with a pair of step-up transformers as illustrated in FIG. 1 when a line surge occurs will ground both lines virtually simultaneously because either line igniting the gas tube 13 will provide a low impedance path for both lines through electrode 16.

FIG. 2 illustrates a single line signal line or a double line where one line is grounded. Signal line 30 feeds utilization device 32. Electrode 33 in gas-filled discharge tube 34 is connected to signal line 30 and through transformer 35 to electrode 36. Electrode 37 is connected to electrical ground. The step-up transformer 35 is similar to transformers l9 and in FIG. 1 and the circuit of FIG. 2 operates similar to that of either half of the circuit of FIG. 1. The turns ratio for transformer 35 are selected in the same manner as those chosen for the transformers in FIG. 1. In this fashion a signal of sufficient magnitude appearing on signal line will cause the gas tube 34 to fire thereby bringing signal line 30 through electrodes 33 and 37 down to electrical ground thereby arresting the pulse and preventing it from reaching the utilization device. A signal of acceptable magnitude will 'not cause the tube to fire but will be allowed to travel down the line.

We claim:

1. For a lightning protector for a pair of electrical sig nal lines coupled to a utilization device, in combination: a gas-filled discharge tube having five electrodes, one of said electrodes adapted for electrical connection to one of said signal lines, another of said electrodes adapted for electrical connection to the other of said signal lines, and a third electrode being electrically grounded; a first step-up transformer connected between said one electrode and a fourth electrode; and another step-up transformer connected between said another electrode and a fifth electrode.

2. The invention as in claim 1 wherein the gas discharge tube has an ignition potential value substantially greater than the amplitude of the normal signals on said signal lines; and the turns ratio of said transformers are such that the potential appearing between said one and said fourth electrode and between said another and said fifth electrode through the respective transformers is less than the ignition potential when the normal signal appears on the signal lines but is at least equal to the ignition potential when the amplitude of a signal on ei- 4 ther signal line is greater than that of the normal signa to a degree sufficient to be damaging to the utilization device.

3. For a lightning protector for an electrical signal line coupled to a utilization device: a gas-filled discharge tube having at least three electrodes, one of said electrodes adapted for electrical connection to the signal line; another of said electrodes electrically grounded; and a transformer having a step-up turns 'ratio connected between said one electrode and the third ungrounded electrode withthe transformerprimary and secondary connected in series aiding relationship.

. 4. The invention as set forth in claim 3 wherein the gas discharge tube has an ignition potential value substantially greater than the amplitude of the normal signal on said signal line; and the turns ratio of said transformer is such that the potential appearing between said one and said third electrode through the transformer is less than the ignition potential when the normal signal appears on the signal line but is at least equal to the ignition potential when the amplitude of a signal on the signal line is great enough to damage the utilization device.

5. The invention as set forth in claim 4 wherein the ignition potential of said gas discharge tube is in the order of about 200 volts or greater.

6. In lightning protector for a pair of electrical signal lines coupled to a utilization device which includes a gas-filled three-electrode discharge tube with one electrode electrically grounded and each of the other two electrodes connected to respective ones of said signal lines, the improvement comprising: another electrode in the gas tube for each electrode connected to a signal line; a step-up transformer coupled between each of said another electrodes and its associated lineconnected electrode, the turns ratio of said transformers being selected such that the potential appearing between the transformer-coupled electrodes is less than the gas ignition potential when a normal signal level is on the lines but at least reaches the gas ignition potential when a line signal reaches a level sufficient to damage the utilization device.

Disclaimer 3,816,802.R0;2 I. 0711870, Edina and TV'z'ZZZam- Z fi'ger'er, Minneapolis, Minn. LIGHTNING ARRESTER. Patent dated June 11, 1974. Disclaimer filed Mar. 28, 1975, by the assignee, Buckbee MeaT-s Company. Hereby enters this disclaimer to claims 1, 2, 3, 4, 5 and 6 of said patent.

[Ofiicial Gazette June 24, 1975.]

Disclaimer 3,816,802.l?0;1 l. Owls-7c, Edina and TVz'ZZz'am- D. Eger-er, Minneapolis, Minn. LIGHTNING ARRESTER. Patent dated June 11, 1974. Disclaimer filed Mar. 28, 1975, by the assignee, Buclcbee Mears Uompawy. Hereby enters this disclaimer to claims 1, 2, 3, 4, 5 and 6 of said patent.

[Ofiicial Gazette June 24, 1,975.] 

1. For a lightning protector for a pair of electrical signal lines coupled to a utilization device, in combination: a gasfilled discharge tube having five electrodes, one of said electrodes adapted for electrical connection to one of said signal lines, another of said electrodes adapted for electrical connection to the other of said signal lines, and a third electrode being electrically grounded; a first step-up transformer connected between said one electrode and a fourth electrode; and another step-up transformer connected between said another electrode and a fifth electrode.
 2. The invention as in claim 1 wherein the gas discharge tube has an ignition potential value substantially greater than the amplitude of the normal signals on said signal lines; and the turns ratio of said transformers are such that the potential appearing between said one and said fourth electrode and between said another and said fifth electrode through the respective transformers is less than the ignition potential when the normal signal appears on the signal lines but is at least equal to the ignition potential when the amplitude of a signal on either signal line is greater than that of the normal signal to a degree sufficient to be damaging to the utilization device.
 3. For a lightning protector for an electrical signal line coupled to a utilization device: a gas-filled discharge tube having at least three electrodes, one of said electrodes adapted for electrical connection to the signal line; another of said electrodes electrically grounded; and a transformer having a step-up turns ratio connected between said one electrode and the third ungrounded electrode with the transformer primary and secondary connected in series aiding relationship.
 4. The invention as set forth in claim 3 wherein the gas discharge tube has an ignition potential value substantially greater than the amplitude of the normal signal on said signal line; and the turns ratio of said transformer is such that the potential appearing between said one and said third electrode through the transformer is less than the ignition potential when the normal signal appears on the signal line but is at least equal to the ignition potential when the amplitude of a signal on the signal line is great enough to damage the utilization device.
 5. The invention as set forth in claim 4 wherein the ignition potential of said gas discharge tube is in the order of about 200 volts or greater.
 6. In lightning protector for a pair of electrical signal lines coupled to a utilization device which includes a gas-filled three-electrode discharge tube with one electrode electrically grounded and each of the other two electrodes connected to respective ones of said signal lines, the improvement comprising: another electrode in the gas tube for each electrode connected to a signal line; a step-up transformer coupled between each of said another electrodes and its associated line-connected electrode, the turns ratio of said transformers being selected such that the potential appearing between the transformer-coupled electrodes is less than the gas ignition potential when a normal signal level is on the lines but at least reachEs the gas ignition potential when a line signal reaches a level sufficient to damage the utilization device. 